There has been an increasing need for the electron/ion beam equipment that can be operated at low voltages. The cold field emitter (CFE) provides a stable electron beam and has a long lifetime for conventional electron microscopy and electron beam lithography. Cold field-emission cathode units produce electron beams with higher current density and with lower energy spread than thermionic cathodes.
A cold field emitter for producing an electron beam includes at least one cold cathode unit. Each of the cold cathode units includes an emitter cone having an emitter tip and a gate spaced apart from the emitter tip for extracting electrons from the emitter tip in a propagation direction upon application of a positive dc voltage on the gate with respect to the emitter tip. Each of the cold cathode units also includes a lens electrode disposed further in the propagation direction from the emitter tip than the gate for focusing the extracted electrons in the propagation direction. The emitter tip may be a single crystal tungsten tip. Single crystal hafnium carbides (HfC) and other metal carbides (TiC, NbC, etc) are used as alternative to W for the use as an electron emitter.
Conventional electron generation systems using cold field emitters with W or HfC tips are based on the operation of the tips until states of instability are arrived at. These instabilities, which are typically caused by surface contamination, result in increased current ultimately causing tip failure. Therefore once the beam current starts to demonstrate instabilities, the tip is flashed with a long settling time and the process is refreshed.
The current operating modes of the conventional electron generation system result in extended down time between tip flash to allow for beam stabilization. In addition, to reduce the rate of contamination adsorption on tip surface, ultra high vacuum (UHV) is required.
It is within this context that embodiments of the present invention arise.